1. Field of the Invention
This invention relates generally to support structures, and more particularly, to an improved house jack in form of a kit for the temporary support of building joists.
2. Description of the Prior Art
There are a variety of devices presently known in the art used for temporary support of building joists. The most commonly employed support is the house jack. A conventional house jack is an inverted cone shaped device having an enlarged footprint leading to a narrow neck. The neck is threaded for acceptance of a jack screw that can be telescoped upwardly. Operation of the house jack requires placing the jack on beneath a building joist. An extension device, typically a 4.times.4 timber, is then placed on top of the jack screw to span the distance between the jack and the joist to be lifted. Typically a number of joists are lifted simultaneously by placing a second beam across the top of the timber. The adjustability of the jack is then used to raise the timber which in turn raises the beam and finally the joists.
A problem with the conventional house jack is that it can be dangerous to operate. For instance, the use of a 4.times.4 timber to exert ten tons of force requires the wood to be in perfect condition. In reality all wood has minute cracks, warpage, or the like latent conditions that may propagate into a catastrophic failure under stress. To complicate the matter, unless the beam and jack combination is perfectly aligned, an off center loading can cause both the timber and jack to unexpectedly hurtle across the floor. To help prevent such misalignment the operator needs to use a liquid level or plumb for alignment, either process is difficult due to the weight of the extension timber and practically impossible if the operator is without the assistance of fellow workers.
Another problem with conventional house jacks is that they are typically made cast iron or filled with concrete or the like for stability. The weight of the jack makes it difficult to transport and place into position.
Yet another problem arises if the operator of the house jack relies upon a 2.times.4 timber to provide extension support. The 2.times.4 is more readily available at a job site than the 4.times.4 yet has obvious weaknesses. More commonplace is the use of two 2.times.4's nailed together to make a 4.times.4, the use of a double board providing little more than a false sense of security. Since more than one joist is required to be lifted, the beam placed across the top of the extension timber further complicates the aforementioned operation. All the problems with the extension timber apply to the cross support beam.
Yet still another problem with the conventional house jacks is the jack operating location. Typically the house jack is less than two feet in height requiring jack adjustment to be made within the two foot span. This position forces the operator into an unnatural stance requiring the operator to use lower back muscles or otherwise place a strain on the body for jack operation. Since the operator will have a natural reaction to stand upright, an imbalance to the timber can occur when the operator attempts to operate the jack from an upright position, i.e., operating the jack by foot.
U.S. Pat. No. 3,222,030 issued to Thorpe discloses a permanent floor structure support utilizing two co-planar plates having a threaded engagement adjustment mechanism. The Thorpe device cannot span a building joist with the use of an additional extension. If the adjustment mechanism is made solid, the device would be to top heavy thus requiring the support base to remain hollow. If the support base is enlarged, adjustment must be made at the top of the structure causing the operator to make operate over his head. Any attempt to exert pressure while working over the operators head can result in injury as previously mentioned.
Another structural support device is disclosed in U.S. Pat. No. 3,655,161, issued to Schueler. The Schueler device is a post shore having a means for rough adjustment as well as fine adjustment. The device is complicated and made for permanent installation. Disadvantages of adjustment is duplicated in the Schueler device requiring adjustment at the bottom as well as the top of the structure making both positions difficult to adjust. Schueler illustrates the need for a stable base by disclosing the use of anchor bolts fastened through the bottom plate.
Therefore, there exists a need for a support structure kit capable of installation without the need for additional shoring such as timbers; a structure that is self aligning; adjustable at a location that is safe for the operator; reduces the opportunity for injury; and dissembles for ease of portability and storage.